DESCRIPTION: The overall goal of this study is to investigate time-dependent reliability of bilayer and tri-layer Dental ceramic structures. Input of stresses computed from finite element analysis (Aim 1) into the new Version 6.1 NASA CARES/Life software (Ceramic Analysis and Reliability Evaluation of Structures/Life) used in Aims 3 and 4 will yield survival probabilities of metal/ceramic and ceramic/ceramic structures as a function of thermal contraction mismatch, geometry, surface treatment, and heat treatment effects. Specific Aim 2 is focused on the effect of three thermal treatments on residual stresses and the impact of cyclic loading on the flexural strength of thermally compatible and thermally incompatible bilayer ceramic-based structures. Correlations will be investigated between thermal mismatch stresses within the interfacial region and surface of ceramic/ceramic laminates computed from microhardness indentation cracks and stresses predicted from finite element analysis based on dilatometry and viscosity data. We will optimize heat treatment options to enhance the residual stress distribution for a known thermally incompatible core ceramic/veneer ceramic system. CARES/Life analyses will be performed in Aim 3 based on data from Aims 1 and 2 to determine the delayed failure reliability of ceramic bars and bridges made from a thermally compatible and thermally incompatible core ceramic/veneer ceramic system. The influence of interfacial defects (Aim 4) on time-dependent reliability will also be analyzed for a lithia-disilicate-based glass-ceramic core with a glass veneer that has exhibited veneer spallation clinically and an yttria-stabilized zirconia core/veneer system known to be susceptible to interfacial delamination. Aim 4 will also analyze the interfacial toughness and interfacial fracture characteristics of two defective ceramic/ceramic structures and the time-dependent strength of the two bilayer structures based on CARES-Life analysis. This study should yield clinically-relevant fatigue data and an improved method for assessing the time-dependent survival probability of ceramic prostheses.